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.TH T_RCVUDATA 3NSL "Oct 22, 2014"
.SH NAME
t_rcvudata \- receive a data unit
.SH SYNOPSIS
.LP
.nf
#include <xti.h>



\fBint\fR \fBt_rcvudata\fR(\fBint\fR \fIfd\fR, \fBstruct t_unitdata *\fR\fIunitdata\fR, \fBint *\fR\fIflags\fR);
.fi

.SH DESCRIPTION
.sp
.LP
This routine is part of the \fBXTI\fR interfaces which evolved from the
\fBTLI\fR interfaces. \fBXTI\fR represents the future evolution of these
interfaces. However, \fBTLI\fR interfaces are supported for compatibility. When
using a \fBTLI\fR routine that has the same name as an \fBXTI\fR routine, the
\fBtiuser.h\fR header file must be used.  Refer to the  \fBTLI\fR
\fBCOMPATIBILITY\fR section for a description of differences between the two
interfaces.
.sp
.LP
This function is used in connectionless-mode to receive a data unit from
another transport user. The argument \fIfd\fR identifies the local transport
endpoint through which data will be received, \fIunitdata\fR holds information
associated with the received data unit, and \fIflags\fR is set on return to
indicate that the complete data unit was not received. The argument
\fIunitdata\fR points to a \fBt_unitdata\fR structure containing the following
members:
.sp
.in +2
.nf
\fBstruct netbuf addr;
struct netbuf opt;
struct netbuf udata;\fR
.fi
.in -2

.sp
.LP
The \fImaxlen\fR field of \fIaddr\fR, \fIopt\fR and \fIudata\fR must be set
before calling this function to indicate the maximum size of the buffer for
each. If the  \fImaxlen\fR field of  \fIaddr\fR or  \fIopt\fR is set to zero,
no information is returned in the  \fIbuf\fR field of this parameter.
.sp
.LP
On return from this call, \fIaddr\fR specifies the protocol address of the
sending user, \fIopt\fR identifies options that were associated with this data
unit, and \fIudata\fR specifies the user data that was received.
.sp
.LP
By default, \fBt_rcvudata()\fR operates in synchronous mode and will wait for a
data unit to arrive if none is currently available. However, if
\fBO_NONBLOCK\fR is set by means of  \fBt_open\fR(3NSL) or \fBfcntl\fR(2),
\fBt_rcvudata()\fR will execute in asynchronous mode and will fail if no data
units are available.
.sp
.LP
If the buffer defined in the \fIudata\fR field of \fIunitdata\fR is not large
enough to hold the current data unit, the buffer will be filled and
\fBT_MORE\fR will be set in \fIflags\fR on return to indicate that another
\fBt_rcvudata()\fR should be called to retrieve the rest of the data unit.
Subsequent calls to \fBt_rcvudata()\fR will return zero for the length of the
address and options until the full data unit has been received.
.sp
.LP
If the call is interrupted, \fBt_rcvudata()\fR will return \fBEINTR\fR and no
datagrams will have been removed from the endpoint.
.SH RETURN VALUES
.sp
.LP
Upon successful completion, a value of  \fB0\fR is returned.  Otherwise, a
value of  \(mi1 is returned and \fBt_errno\fR is set to indicate an error.
.SH VALID STATES
.sp
.LP
\fBT_IDLE\fR.
.SH ERRORS
.sp
.LP
On failure, \fBt_errno\fR is set to one of the following:
.sp
.ne 2
.na
\fB\fBTBADF\fR\fR
.ad
.RS 15n
The specified file descriptor does not refer to a transport endpoint.
.RE

.sp
.ne 2
.na
\fB\fBTBUFOVFLW\fR\fR
.ad
.RS 15n
The number of bytes allocated for the incoming protocol address or options
\fI(maxlen)\fR is greater than  \fB0\fR but not sufficient to store the
information. The unit data information to be returned in \fIunitdata\fR will be
discarded.
.RE

.sp
.ne 2
.na
\fB\fBTLOOK\fR\fR
.ad
.RS 15n
An asynchronous event has occurred on this transport endpoint and requires
immediate attention.
.RE

.sp
.ne 2
.na
\fB\fBTNODATA\fR\fR
.ad
.RS 15n
\fBO_NONBLOCK\fR was set, but no data units are currently available from the
transport provider.
.RE

.sp
.ne 2
.na
\fB\fBTNOTSUPPORT\fR\fR
.ad
.RS 15n
This function is not supported by the underlying transport provider.
.RE

.sp
.ne 2
.na
\fB\fBTOUTSTATE\fR\fR
.ad
.RS 15n
The communications endpoint referenced by  \fIfd\fR is not in one of the states
in which a call to this function is valid.
.RE

.sp
.ne 2
.na
\fB\fBTPROTO\fR\fR
.ad
.RS 15n
This error indicates that a communication problem has been detected between XTI
and the transport provider for which there is no other suitable XTI error
\fB(t_errno)\fR.
.RE

.sp
.ne 2
.na
\fB\fBTSYSERR\fR\fR
.ad
.RS 15n
A system error has occurred during execution of this function.
.RE

.SH TLI COMPATIBILITY
.sp
.LP
The \fBXTI\fR and \fBTLI\fR interface definitions have common names but use
different header files. This, and other semantic differences between the two
interfaces are described in the subsections below.
.SS "Interface Header"
.sp
.LP
The \fBXTI\fR interfaces use the header file, \fBxti.h\fR. \fBTLI\fR interfaces
should \fInot\fR use this header.  They should use the header:
.br
.in +2
#include <tiuser.h>
.in -2
.SS "Error Description Values"
.sp
.LP
The \fBt_errno\fR values that can be set by the \fBXTI\fR interface and cannot
be set by the \fBTLI\fR interface are:
.br
.in +2
\fBTPROTO\fR
.in -2
.br
.in +2
\fBTOUTSTATE\fR
.in -2
.sp
.LP
A \fBt_errno\fR value that this routine can return under different
circumstances than its \fBXTI\fR counterpart is \fBTBUFOVFLW.\fR It can be
returned even when the \fBmaxlen\fR field of the corresponding buffer has been
set to zero.
.SS "Option Buffers"
.sp
.LP
The format of the options in an \fBopt\fR buffer is dictated by the transport
provider. Unlike the \fBXTI\fR interface, the \fBTLI\fR interface does not fix
the buffer format.
.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7)  for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
MT Level	Safe
.TE

.SH SEE ALSO
.sp
.LP
.BR fcntl (2),
.BR t_alloc (3NSL),
.BR t_open (3NSL),
.BR t_rcvuderr (3NSL),
.BR t_sndudata (3NSL),
.BR attributes (7)
